Genetics is an amazing thing; it makes us who we are. Inherited genes from each of our parents determine whether we are male or female, the colour of our hair and eyes, and even our personality traits. Sounds simple but it is quite complex.
Genes are made up of DNA, which is made up of chromosomes. Normally we inherit 23 sets of chromosomes from our mother and 23 sets from our father. However, sometimes things go awry. An example of this is Down syndrome, a condition caused by the presence of an extra chromosome: chromosome 21. Down syndrome, also known as trisomy 21, is the most common of chromosomal abnormalities and affects around one in 1,000 babies each year. It was first described in 1866 by a British doctor, John Langdon Down, after whom it is named. It was not until 1959, however, that the genetic link was discovered. There are three known types of Down syndrome:
• Trisomy 21 – where every cell in the body has an extra copy of chromosome 21;
• Translocation Down syndrome – where cells have an extra part of chromosome 21 or where a whole copy of chromosome is attached to another chromosome rather than on its own;
• Mosaic Down syndrome where only some cells have an extra chromosome 21.
In many cases, Down syndrome affects physical growth and intellect but more often it is distinguished by its recognisable physical characteristics. Although babies with Down syndrome are usually born at average weight and size, their growth rate is slower. This is also noticeable in adults who tend to have a shorter stature.
Other common signs can vary among individuals but include having a small chin, almond-shaped eyes, a flat nasal bridge, a protruding large tongue in a small mouth cavity, and a single crease on the palm. Another early distinguishing feature is low muscle tone. This can make babies and toddlers appear floppy, often making it difficult for them to lift their head up at the expected developmental milestone of around six weeks old.
Developmental milestones are markers used as a guide to monitor specific stages that babies are expected to reach by a certain age. For example, crawling typically occurs between 6-12 months but may not happen until 8-22 months in a child with Down syndrome. Low muscle tone can also affect suckling and feeding that could also account for low weight after birth.
Intellectual ability, reasoning, thinking, understanding and social skills may be affected as well as speech problems. However, if speech is affected, it may not be because of intellect; it may be due to the size of the tongue. As well as problems associated directly with Down syndrome, children and adults are also susceptible to a range of health problems which can affect:
• Hearing and Vision;
• Heart;
• Endocrine – for example, thyroid problems and diabetes;
• Immune System;
• Gastrointestinal – Constipation;
• Teeth;
• Fertility.
Doctors do not know what actually triggers the chromosome abnormality that causes Down syndrome, but it is more common in women over 35 having babies or in women who already have a child with the condition. This is why some doctors recommend that every woman should be tested, especially if she is in the higher risk category.
There are two types of test: screening and diagnostic. Screening tests do not confirm whether the child has Down syndrome, only the likelihood. Diagnostic testing provides a firm yes or no, but it comes with a small risk of inducing a miscarriage. In some cases, an ultrasound scan may show abnormalities which may lead to a suspicion of Down syndrome, such as extra fluid in the area of the neck or a small or absent nasal bone. Diagnosis after birth is usually based on physical appearance and, if suspected, the baby’s chromosomes will be tested to confirm diagnosis.
Although there is no cure for Down syndrome, it is important to seek medical guidance for common associated health problems. It is also likely that throughout the child’s life, he or she may need help from other health professionals such as speech and language therapists, occupational therapists and physiotherapists.
Physiotherapy can help improve motor skills and should be started as early as possible if there are indications of developmental delays and low muscle tone.
As mentioned earlier, signs and symptoms can vary greatly between individuals. In recent years, the average life expectancy has risen from 25 years of age in 1983 to currently 60 years of age.
Individuals who are only mildly affected may choose to live independently, work, contribute to the community and form intimate relationships.
